Perhaps this is implicit in what you say, but signaling and social networking benefits from going to an Ivy League may play major roles independently of human capital.

I try to use the phrase "treatment effect" to encompass both capital improvements and social networking, "sheepskin effect" to encompass signalling, and "selection effect" to encompass ability bias. It seems to me that social capital (i.e. knowing other people and them knowing you) could be wrapped into human capital directly without much loss.